Congestion control method, congestion control device, and congestion control program

ABSTRACT

A congestion control method in an IP telephone system includes acquiring a number of simultaneous calls in one line shared by a plurality of IP telephones, acquiring a call time order corresponding to length of a call time for each call, and controlling a packet discard rate of each call on the basis of the number of simultaneous calls and the call time order. The packet discard rate of each call is set to a predetermined first upper limit value or less. In addition, the packet discard rate is set higher as the call time is longer, and the packet discard rate is set lower as the call time is shorter. Further, the packet discard rate of the latest call having the shortest call time is set to be equal to or less than a predetermined second upper limit value lower than the predetermined first upper limit value.

TECHNICAL FIELD

The present invention relates to a technique for controlling congestionin an IP (Internet Protocol) telephone system.

BACKGROUND ART

For recent frequent disasters, it is useful that a plurality of usersuse a wireless channel in which the channel is shared in band to securecommunication in an evacuation site or the like. In addition, with thespread of call applications by smart phones, use demands for not onlydaily call means but also emergency contact means have become high.Since the call application performs real-time communication, packetcommunication by UDP/IP (User Datagram Protocol/Internet Protocol) isperformed. Since retransmission control is not performed in the UDP/IP,when a call traffic equal to or more than a capacity of the wirelesschannel occurs, packets exceeding the capacity are discarded (PTL 1).

In a case of emergency, it is important to accommodate as many calls aspossible (PTL 2). However, in the emergency such as the disaster, thereis a tendency that the call time per person is long and the number ofusers is increased. Thus, the total communication amount of the callapplication exceeds the capacity of the wireless channel, and the packetdiscard rate becomes high, and the call quality is deteriorated (PTL 3).As a result, a call newly originated is not started, a call loss rate isincreased, and the number of call accommodation cannot be increased.

NPL 1 discloses a congestion control technique for suppressing anincrease in the call loss rate. According to the congestion controltechnique, when the total communication amount of the call applicationexceeds the line capacity, priority is set on the basis of the call timelength, and the packet discard rate is set according to the priority.More specifically, the shorter the call time, the higher the priority,and the lower the packet discard rate. On the other hand, the longer thecall time, the lower the priority level and the higher the packetdiscard rate. When the packet discard rate is increased and the callquality is deteriorated, it is expected that such a situation encouragesa user to end the call. Namely, the longer the call time, the morelikely it is that the user ends the call. Ending long calls will free upthe line resources and improves the call quality of other users' calls.Another advantage of the congestion control is that the call loss ratewill decrease because new calls from users are more likely to beaccepted.

In NPL 1, the upper limit value of the packet discard rate is set sothat the call quality is not remarkably deteriorated. The maximum valueof the number of simultaneous calls (the maximum number of simultaneouscalls) is set so that the packet discard rate does not exceed the upperlimit value. For the call newly generated exceeding the maximum numberof simultaneous calls, all packets are discarded to substantially make acall loss.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Patent Application Publication No. 2008-160712-   [PTL 2] Japanese Patent Application Publication No. 2008-219280-   [PTL 3] Japanese Patent Application Publication No. 2014-20970.

Non Patent Literature

-   [NPL 1] Nagase, Ono, Ito, Yoshioka, Osaka, Furuya, Miyagi, Hayashi,    “A study on congestion control technique in emergency communication    by using fixed wireless line”, The Institute of Electronics,    Information and Communication Engineers society conference of 2020,    B-5-82, Sep. 1, 2020

SUMMARY OF INVENTION Technical Problem

Packets exceeding the line capacity of one line shared by a plurality ofIP telephones are discarded. When packets of all the calls using theline are uniformly (equally) discarded, the call quality of all thecalls is uniformly deteriorated. This leads to a lower level ofsatisfaction of all the users, and it is hard to say that this is themost appropriate congestion control.

For example, at the time of the disaster, it is imaginable that a largenumber of users will just want to confirm each other's safety. When thecall time is long, there is a high possibility that necessaryinformation has already been transmitted, but when the call time isshort, the possibility is low. Therefore, it is desired to ensure thecall quality of the call having the short call time, particularly the“latest call” having the shortest call time as much as possible.

According to the technique described in the above-mentioned NPL 1,especially in a situation where the number of simultaneous calls ismaximum, the packet discard rate of the latest call having the shortestcall time becomes considerably high. That is, the call quality of thelatest speech in which good call quality is most desired is alsodeteriorated. From such a viewpoint, there is room for improving thecongestion control.

One object of the present invention is to provide a congestion controltechnique capable of suppressing deterioration in call quality of thelatest call having the shortest speech call in a situation where thenumber of simultaneous call is maximum.

Solution to Problem

A first aspect relates to a congestion control method in an IP telephonesystem.

The congestion control method includes

a processing for acquiring a number of simultaneous calls in one lineshared by a plurality of IP telephones,

a processing for acquiring a call time order corresponding to

a length of the call time for each call, and

a packet discard control processing for controlling a packet discardrate of each call on the basis of the number of simultaneous calls

and the call time order.

In the packet discard control processing,

the packet discard rate of each call is set to be equal to or less thana predetermined first upper limit value,

the packet discard rate is set to be higher as the call time is longer,and the packet discard rate is set to be lower as the call time isshorter, and

the packet discard rate of the latest call having the shortest call timeis set to be equal to or less than a predetermined second upper limitvalue lower than the predetermined first upper limit value.

A second aspect relates to a congestion control program. The congestioncontrol program is executed by a computer, whereby the above congestioncontrol method is implemented by the computer. The congestion controlprogram may be recorded in a computer-readable recording medium. Thecongestion control program may be provided via a network.

A third aspect relates to a congestion control device in the IPtelephone system.

The congestion control device includes an information processing device.

The information processing device is configured to execute a processingfor acquiring a number of simultaneous calls in one line shared by aplurality of IP telephones,

the processing for acquiring the call time order corresponding to thelength of the call time for each call, and

the packet discard control processing for controlling the packet discardrate of each call on the basis of the number of simultaneous calls

and the call time order.

In the packet discard control processing, the information processingdevice sets the packet discard rate of each call to be equal to or lessthan the predetermined first upper limit value, sets the packet discardrate higher as the call time is longer, sets the packet discard ratelower as the call time is shorter, and

sets the packet discard rate of the latest call having the shortest calltime to be equal to or less than the predetermined second upper limitvalue lower than the predetermined first upper limit value.

Advantageous Effects of Invention

According to the present invention, the packet discard rate of each callis set to be equal to or less than the predetermined first upper limitvalue. More particularly, the packet loss rate is set such that thehigher the priority ranking, the lower the packet loss rate, and thelower the priority ranking, the higher the packet loss rate. Further,the packet discard rate of the latest call having the shortest call timeis set to be equal to or less than the predetermined second upper limitvalue lower than the predetermined first upper limit value. Therefore,even in a situation where the number of simultaneous calls becomes themaximum number of simultaneous calls, deterioration in the call qualityof the latest call can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a configuration example of an IPtelephone system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of placement of congestioncontrol devices according to the embodiment of the present invention.

FIG. 3 is a block diagram showing another example of placement of thecongestion control devices according to the embodiment of the presentinvention.

FIG. 4 is a table showing a relationship between a call time order and apacket discard rate in a case of a comparative example.

FIG. 5 is a graph showing the relationship between the call time orderand the packet discard rate in the case of the comparative example.

FIG. 6 is a graph showing the relationship between the line bandwidthand the packet discard rate of the latest call in the case of thecomparative example.

FIG. 7 is a conceptual diagram showing an overview of the packet discardcontrol processing according to the embodiment of the present invention.

FIG. 8 is a conceptual diagram for describing the packet discard controlprocessing according to the embodiment of the present invention.

FIG. 8 is a conceptual diagram for describing the packet discard controlprocessing according to the embodiment of the present invention.

FIG. 10 is a flowchart showing the packet discard control processingaccording to the embodiment of the present invention.

FIG. 11 is a table showing an example of the relationship between thecall time order and the packet discard rate according to the embodimentof the present invention.

FIG. 12 is a graph showing an example of the relationship between thecall time order and the packet discard rate according to the embodimentof the present invention.

FIG. 13 is a graph showing the relationship between the line bandwidthand the packet discard rate according to the embodiment of the presentinvention.

FIG. 14 is a block diagram showing a configuration example of thecongestion control device according to the embodiment of the presentinvention.

FIG. 15 is a block diagram showing a functional configuration example ofthe congestion control device in a base station side according to theembodiment of the present invention.

FIG. 16 is a conceptual diagram showing an example of a call managementtable according to the embodiment of the present invention.

FIG. 17 is a block diagram showing a functional configuration example ofthe congestion control device in a terminal station side according tothe embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention is described below with referenceto the accompanying drawings.

1. IP Telephone System

FIG. 1 is a schematic diagram showing a configuration example of an IPtelephone system 1 according to a present embodiment. The IP telephonesystem 1 includes a base station 10 and a terminal station 20. The basestation 10 is connected to a ground network 2. The terminal station 20is installed, for example, at a disaster prevention related institution,a life related institution, an evacuation place, or the like. The basestation 10 and the terminal station 20 are connected to each other via awireless inter-station line 3 or a wired communication network 4. Thebase station 10 and the terminal station 20 communicate with each othervia the inter-station line 3 or the communication network 4. Theterminal station 20 is connected to a terminal station network 5. Insuch an IP telephone system 1, for example, a user of the ground network2 and a user of the terminal station 20 make a call by the IP telephone.One line of the inter-station line 3 or the communication network 4 isshared by a plurality of IP telephone (calls).

IP telephones use UDP/IP (User Datagram Protocol/Internet Protocol)because real time characteristic is required. Unlike TCP (TransmissionControl Protocol), retransmission is not performed in the UDP/IP.Therefore, when a call traffic exceeds a line capacity of the IPtelephone line, packets exceeding the line capacity are discarded. Forexample, in the IP telephone system 1 shown in FIG. 1 , when the calltraffic exceeds the line capacity of one line of the inter-station line3 or the communication network 4 between the base station 10 and theterminal station 20, the packets exceeding of the line capacity arediscarded.

The IP telephone system 1 according to the present embodimentdynamically controls the packet discard rate of each call in one line.For this purpose, the IP telephone system 1 includes a congestioncontrol device 100. The congestion control device 100 is arranged inassociation with the station (for example, the base station 10 and theterminal station 20) for controlling the communication amount of the IPtelephone.

FIG. 2 is a block diagram showing an example of an arrangement of thecongestion control device 100. In the example shown in FIG. 2 , thecongestion control device 100-1 is arranged in the base station 10, andthe congestion control device 100-2 is arranged in the terminal station20. Each of the congestion control devices 100-1 and 100-2 controls thepacket discard rate in the IP telephone line (the inter-station line 3or communication network 4) between the base station 10 and the terminalstation 20.

FIG. 3 is a block diagram showing another example of the arrangement ofthe congestion control device 100. In the example shown in FIG. 3 , thecongestion control device 100-1 is arranged between the base station 10and the ground network 2, and the congestion control device 100-2 isarranged between the terminal station 20 and the “user of the terminalstation 20”. Even in this case, each of the congestion control devices100-1 and 100-2 can control the packet discard rate in the IP telephoneline (the inter-station line 3 or communication network 4) between thebase station 10 and the terminal station 20.

The congestion control device 100 according to the present embodimentperforms packet discard while appropriately controlling the packetdiscard rate at the time of congestion. This processing is hereinafterreferred to as “packet discard control processing”. Hereinafter, “packetdiscard control processing” by the congestion control device 100 will bedescribed in detail.

2. Comparative Example

In order to clarify the significance of the packet discard controlprocessing according to the present embodiment, a comparative examplewill be first described. The comparative example is based on thetechniques disclosed in the above-mentioned NPL 1.

The number of simultaneous calls j is the number of calls that are usingone line at the same time. For example, the number of simultaneous callsj is the number of calls simultaneously establishing a session at acertain time in the one line of the inter-station line 3 or thecommunication network 4. The line capacity of one line is set to B_(L).Also, a call application band used by one call application is set to By.In this case, the packet discard rate as a whole in one line isexpressed by the following formula (1).

$\begin{matrix}\left\lbrack {{Math}.1} \right\rbrack &  \\{1 - \frac{B_{L}}{j \cdot B_{V}}} & (1)\end{matrix}$

In order to prevent remarkable deterioration of call quality, apredetermined upper limit value is set for the packet discard rate ofeach call. This predetermined upper limit value is hereinafter referredto as “first upper limit value P_(B)”. The first upper limit value P_(B)is 50%, for example. The first upper limit value P_(B) can be said to bea packet discard rate at which the minimum call quality can be obtained.Since the upper limit value of the packet discard rate of each call isthe first upper limit value P_(B), the upper limit value of the packetdiscard rate as a whole in one line is also the first upper limit valueP_(B). A maximum number of simultaneous calls jmax is the maximum valueof the number of simultaneous calls j in which the packet discard rateas a whole in one line is equal to or less than the first upper limitvalue P_(B). The maximum number of simultaneous calls jmax is expressedby the following formula (2).

$\begin{matrix}\left\lbrack {{Math}.2} \right\rbrack &  \\{{j\max} = \left\lfloor {\frac{1}{1 - P_{B}}\frac{B_{L}}{B_{V}}} \right\rfloor} & (2)\end{matrix}$

The right side of the formula (2) is a floor function, and gives amaximum integer equal to or less than an argument. For example, in acase where B_(L)/B_(V)=3.4 is satisfied, and the first upper limit valueP_(B) is 50%, the maximum number of simultaneous calls jmax is 6.

The call time order k is an order representing the length of the calltime. For example, in the following description, the longer the calltime is, the higher the call time order k becomes, and the shorter thecall time is, the lower the call time order k becomes. The call timeorder k of the longest call for call time among the j calls (referred to“first call” below) is 1. The call time order k of the shortest call forcall time among the j calls (referred to “latest call” below) is equalto the number of simultaneous calls j (k=j).

When the total communication amount of the call application exceeds theline capacity B_(L), a packet discard rate D_(j,k) is set for each call.The packet discard rate D_(j,k) is set on the basis of the number ofsimultaneous calls j and the call time order k of each call. Moreparticularly, the packet discard rate D_(j,k) is set to be higher as thecall time order k is higher, and the packet discard rate D_(j,k) is setto be lower as the call time order k is lower. When the packet discardrate D_(j,k) is increased and the call quality is deteriorated, it isexpected that such a situation encourages a user to end the call.Namely, the longer the call time, the more likely it is that the userends the call. Ending long calls will free up the line resources andimproves the call quality of other users' calls. Another advantage ofthe congestion control is that the call loss rate will decrease becausenew calls from users are more likely to be accepted.

.

FIGS. 4 and 5 show an example of the relationship between the call timerank k and the packet discard rate D_(j,k) in the comparative example.In this example, B_(L)/B_(V)=3.4, the first upper limit value P_(B)=50%,and the maximum number of simultaneous calls jmax=6 are satisfied. Whenthe number of simultaneous calls j is 1 to 3, no packet is discarded.When the number of simultaneous calls j is 4 or more, some packets arediscarded. As shown in FIGS. 4 and 5 , the packet discard rate D_(j,k)is set to be higher as the call time order k is higher, and the packetdiscard rate D_(j,k) is set to be lower as the call time order k islower. In particular, as can be seen from FIG. 5 , the packet discardrate D_(j,k) is set so as to change linearly with respect to the calltime order K. In other words, the packet discard rate D_(j,k) is set sothat the relationship between the call time order k and the packetdiscard rate D_(j,k) is directly proportional to each other. the packetdiscard rate D_(j,k) in the comparative example is expressed by thefollowing formula group.

<In the Case of Condition A>

A condition A is that the number of simultaneous calls j is expressed bythe following formula (3). In the case of condition A, the totalcommunication amount of the call application does not exceed the linecapacity B_(L). Therefore, the packet discard rate D_(j,k) of eachpacket is 0. In the example shown in FIG. 4 , the case of J=1 to 3corresponds to the case of condition A.

$\begin{matrix}\left\lbrack {{Math}.3} \right\rbrack &  \\{0 \leqq j \leqq \frac{B_{L}}{B_{V}}} & (3)\end{matrix}$

<In the Case of Condition B>

The condition B is that the number of simultaneous calls j is expressedby the following formula (4). In the case of condition B, the packetdiscard rate D_(j,k), of each call is expressed by the following formula(5). In the case of condition B, the packet discard rate D_(j,k) of thefirst call (k=1) having the highest call time order k is equal to orless than the first upper limit value P_(B). Further, as can be seenfrom the formula (5), the packet discard rate D_(j,k) of the latest call(k=j) having the lowest call time order k is set to 0. In the examplesshown in FIGS. 4 and 5 , the case of j=4 corresponds to the case ofcondition B.

$\begin{matrix}\left\lbrack {{Math}.4} \right\rbrack &  \\{\left\lfloor {B_{L}/B_{V}} \right\rfloor < j \leqq \left\lfloor {\frac{B_{L}}{B_{V}}\frac{2}{\left( {2 - P_{B}} \right)}} \right\rfloor} & (4)\end{matrix}$ $\begin{matrix}\left\lbrack {{Math}.5} \right\rbrack &  \\{D_{j,k} = {\frac{2\left( {j - \frac{B_{L}}{B_{V}}} \right)}{j\left( {j - 1} \right)}\left( {j - k} \right)}} & (5)\end{matrix}$

<In the Case of Condition E>

The condition E is that the number of simultaneous calls j is expressedby the following formula (6). In the case of condition E, the packetdiscard rate D_(j,k), of each call is expressed by the following formula(7). As can be seen from the formula (7), the packet discard rateD_(j,k) of the first call (k=1) having the highest call time order k isthe first upper limit value P_(B). In the examples shown in FIGS. 4 and5 , the case of j=5 and 6 corresponds to the case of condition E.

$\begin{matrix}\left\lbrack {{Math}.6} \right\rbrack &  \\{\left\lfloor {\frac{B_{L}}{B_{V}}\frac{2}{\left( {2 - P_{B}} \right)}} \right\rfloor < j < \left\lfloor {\frac{1}{1 - P_{B}}\frac{B_{L}}{B_{V}}} \right\rfloor} & (6)\end{matrix}$

Next, a situation in which the number of simultaneous calls j becomesthe maximum number of simultaneous calls jmax will be considered. Fromthe above formula (7), it can be seen that the packet discard rateD_(jmax, jmax) of the latest call (k=jmax) having the lowest call timerank k is represented by the following formula (8).

$\begin{matrix}\left\lbrack {{Math}.8} \right\rbrack &  \\{D_{j{\max,{j\max}}} = \left( {{- P_{B}} - \frac{2B_{L}}{j{\max \cdot B_{V}}} + 2} \right)} & (8)\end{matrix}$

FIG. 6 is a conceptual diagram showing the relationship between the linebandwidth (B_(L)/B_(V)) and the packet discard rate D_(jmax, jmax) ofthe latest call in the case of the maximum number of simultaneous callsjmax. The horizontal axis represents the line bandwidth B_(L)/B_(V), andthe vertical axis represents the packet discard rate D_(jmax, jmax) ofthe latest call. For example, when the line bandwidths are 1.6, 2.1, and2.6, the packet discard rate D_(jmax, jmax) of the latest call are43.3%, 45%, and 46%, respectively. In other words, the packet discardrate D_(jmax, jmax) of the latest call is also considerably high, and isconsiderably close to the first upper limit value P_(B) corresponding tothe minimum call quality.

For example, at the time of the disaster, it is imaginable that a largenumber of users will just want to confirm each other's safety. When thecall time is long, there is the high possibility that necessaryinformation has already been transmitted, but when the call time isshort, the possibility is low. Therefore, it is desired to ensure thecall quality of the call having the short call time, particularly thelatest call having the shortest call time as much as possible.

3. Packet Discard Processing

Hereinafter, the packet discard processing by the congestion controldevice 100 according to the present embodiment will be described indetail. The packet discard control processing according to the presentembodiment can suppress the deterioration in the call quality of thelatest call which occurs in the case of the above-described comparativeexample.

3-1. Overview

FIG. 7 is a conceptual diagram showing an overview of The packet discardcontrol processing according to the present embodiment. FIG. 7 shows therelationship between the call time order k and the packet discard rateD_(j,k) of each call.

Also in the present embodiment, the congestion control device 100 sets(limits) the packet discard rate D_(j,k) of each call to thepredetermined first upper limit value P_(B) or less. More particularly,the congestion control device 100 sets the packet discard rate D_(j,k)to be higher as the call time order k is higher, and the congestioncontrol device 100 sets the packet discard rate D_(j,k) to be lower asthe call time order k is lower.

Further, the congestion control device 100 sets the packet discard rateD k of the latest call (k=j) to be lower as compared with the case ofthe comparative example. Instead, the congestion control device 100increases the packet discard rate D_(j,k) of the call whose call timeorder k is middle as compared with the case of the comparative example.As a result, the function of the packet discard rate D_(j,k) withrespect to the call time order k is convex upward.

More specifically, according to the present embodiment, in order tosuppress the deterioration in the call quality of the latest call,regarding the packet discard rate D_(j,k) of the latest call, an upperlimit value different from the first upper limit value P_(B) isseparately set. The predetermined upper limit value for the packetdiscard rate D_(j,k) of the latest call is hereinafter referred to“second upper limit value P_(C)”. The second upper limit value P_(C) ishigher than 0 and lower than the first upper limit value P_(B). Thepredetermined second upper limit value P_(C) is used as a target whenthe packet discard rate D_(j,k) of the latest call is made lower thanthat in the case of the comparative example. That is, the congestioncontrol device 100 sets (limits) the packet discard rate D_(j,k) of thelatest call to be equal or less than the predetermined second upperlimit value P_(C) lower than the predetermined first upper limit valueP_(B).

Even in a situation where the number of simultaneous calls j becomes themaximum number of simultaneous calls jmax, the packet discard rateD_(j,k) of the latest call is set (limited) to the second upper limitvalue P_(C) or less. Therefore, even in a situation where the number ofsimultaneous calls j becomes the maximum number of simultaneous callsjmax, the deterioration in the call quality of the latest call can besuppressed.

3-2. Example of Packet Discard Rate for Each Condition

FIGS. 8 and 9 are conceptual diagrams for describing the packet discardcontrol processing according to the present embodiment. Morespecifically, FIGS. 8 and 9 show examples of setting the packet discardrate D_(j,k) for each condition.

<In the Case of Condition A>

The condition A is that the number of simultaneous calls j is expressedby the above formula (3). In the case of condition A, the totalcommunication amount of the call application does not exceed the linecapacity B_(L). Therefore, the packet discard rate D_(j,k) of eachpacket is 0. This is the same as in the above-mentioned comparativeexample.

<In the Case of Condition B>

The condition B is that the number of simultaneous calls j is expressedby the above formula (4). In the case of condition B, the packet discardrate is D_(j,k) of each call is expressed by the above formula (5). Inthe case of the condition B, the packet discard rate D_(j,k) of thefirst call (k=1) having the highest call time order k is equal to orless than the first upper limit value P_(B). Further, as can be seenfrom the formula (5), the packet discard rate D_(j,k) of the latest call(K=j) is set to 0. As shown in FIG. 8 , the packet discard rate D_(j,k)is set so as to change linearly with respect to the call time order K.This is the same as in the above-mentioned comparative example.

<In the Case of Condition C>

The condition C is that the number of simultaneous calls j is expressedby the following formula (9). In the case of condition C, the packetdiscard rate D_(j,k) of the first call (k=1) by the comparative examplereaches the first upper limit value P_(B), and the packet discard rateD_(j,k) of the latest call (k=j) by the comparative example is higherthan 0 and equal to or lower than the second upper limit value P_(C). Inthe case of this condition C, the packet discard rate D_(j,k) of eachcall is expressed by the following formulas (10) and (11).

$\begin{matrix}\left\lbrack {{Math}.9} \right\rbrack &  \\{\left\lfloor {\frac{B_{L}}{B_{V}}\frac{2}{\left( {2 - P_{B}} \right)}} \right\rfloor < j \leqq \left\lfloor {\frac{4}{4 - {3P_{B}}}\frac{B_{L}}{B_{V}}} \right\rfloor} & (9)\end{matrix}$ $\begin{matrix}\left\lbrack {{Math}.10} \right\rbrack &  \\{D_{j,k} = {P_{B} - {{P_{B} \cdot \exp}\left( {- {v\left( {j - k} \right)}} \right)}}} & (10)\end{matrix}$ $\begin{matrix}\left\lbrack {{Math}.11} \right\rbrack &  \\{{\exp{\left( {- v} \right)\left\lbrack {1 - {\exp\left\{ {{- \left( {j - 1} \right)}v} \right\}}} \right\rbrack}} = {\left\{ {1 - {\exp\left( {- v} \right)}} \right\}\left\{ {\frac{{j\left( {P_{B} - 1} \right)} + {B_{L}/B_{V}}}{P_{B}} - 1} \right\}}} & (11)\end{matrix}$

As can be seen from the formula (10), the packet discard rate D_(j,k) ofthe latest call (k=j) is set to 0. That is, the packet discard rateD_(j,k) of the latest call is lower than that of the comparativeexample, and is lower than the second upper limit value P_(C) (refer toFIG. 9 ). Further, as shown in FIG. 9 , the function of the packetdiscard rate D_(j,k) with respect to the call time order k is convexupward.

<In the Case of Condition D>

The condition D is that the number of simultaneous calls j is expressedby the following formula (12). In the case of condition D, the packetdiscard rate D_(j,k) of the first call (k=1) of the comparative examplereaches the first upper limit value P_(B), and the packet discard rateD_(j,k) of the latest call (k=j) of the comparative example exceeds thesecond upper limit value P_(C). In the case of this condition D, thepacket discard rate D_(j,k) of each call is expressed by the followingformulas (13) and (14).

$\begin{matrix}\left\lbrack {{Math}.12} \right\rbrack &  \\{\left\lfloor {\frac{4}{4 - {3P_{B}}}\frac{B_{L}}{B_{V}}} \right\rfloor < j < \left\lfloor {\frac{1}{1 - P_{B}}\frac{B_{L}}{B_{V}}} \right\rfloor} & (12)\end{matrix}$ $\begin{matrix}\left\lbrack {{Math}.13} \right\rbrack &  \\{D_{j,k} = {P_{B} - {{\left( {P_{B} - P_{C}} \right) \cdot \exp}\left( {- {v^{\prime}\left( {j - k} \right)}} \right)}}} & (13)\end{matrix}$ $\begin{matrix}\left\lbrack {{Math}.14} \right\rbrack &  \\{{\exp{\left( {- v^{\prime}} \right)\left\lbrack {1 - {\exp\left\{ {{- \left( {j - 1} \right)}v^{\prime}} \right\}}} \right\rbrack}} = {\left\{ {1 - {\exp\left( {- v^{\prime}} \right)}} \right\}\left\{ {\frac{{j\left( {P_{B} - 1} \right)} + {B_{L}/B_{V}}}{P_{C}} - 1} \right\}}} & (14)\end{matrix}$

As can be seen from the formula (13), the packet discard rate D_(j,k) ofthe latest call (k=j) is set to the second upper limit value P_(C). Thatis, the packet discard rate D_(j,k) of the latest call is lower thanthat of the comparative example, And is equal to or less than the secondupper limit value P_(C) (refer to FIG. 9 ). Further, as shown in FIG. 9, the function of the packet discard rate D_(j,k) with respect to thecall time order k is convex upward.

In this way, the packet discard rate D_(j,k) of the latest call is set(limited) to be equal to or less than the predetermined second upperlimit value P_(C). Therefore, even in a situation where the number ofsimultaneous calls j becomes the maximum number of simultaneous callsjmax, the deterioration in the call quality of the latest call can besuppressed.

3-3. Processing Flow

FIG. 10 is a flowchart showing the packet discard control processingaccording to the present embodiment.

In a step S10, the congestion control device 100 judges whether or not apacket has arrived. When the packet arrives (Yes; in step S10), theprocessing proceeds to a step S20.

In a step S20, the congestion control device 100 acquires information onthe number of simultaneous calls j and the call time order k of eachcall.

In a step S100, the congestion control device 100 judges whether or nota condition A (refer to formula (3)) is satisfied. When the condition Ais satisfied (Yes; in step S100), the congestion control device 100 doesnot discard packets (step S150). On the other hand, when the condition Ais not satisfied (No; in step S100), the processing proceeds to a stepS200.

In a step S200, the congestion control device 100 judges whether or nota condition B (refer to formula (4)) is satisfied. When the condition Bis satisfied (Yes; in step S200), the congestion control device 100performs a first packet discard control (step S250). Specifically, thecongestion control device 100 sets the packet discard rate D_(j,k) ofeach call in accordance with the above formula (5), and performs thepacket discard in accordance with the packet discard rate D_(j,k). Onthe other hand, when the condition B is not satisfied (No; in stepS200), the processing proceeds to a step S300.

In a step S300, the congestion control device 100 judges whether or nota condition C (refer to formula (9)) is satisfied. When the condition Cis satisfied (Yes; in step S300), the congestion control device 100performs a second packet discard control (step S350). Specifically, thecongestion control device 100 sets the packet discard rate D_(j,k) ofeach call in accordance with the above formulas (10) and (11), andperforms the packet discard in accordance with the packet discard rateD_(j,k). On the other hand, when the condition C is not satisfied (No;in step S300), the processing proceeds to a step S400.

In a step S400, the congestion control device 100 judges whether or nota condition D (refer to formula (12)) is satisfied. When the condition Dis satisfied (Yes; in step S400), the congestion control device 100performs a third packet discard control (step S450). Specifically, thecongestion control device 100 sets the packet discard rate D_(j,k) ofeach call in accordance with the above formulas (13) and (14), andperforms the packet discard in accordance with the packet discard rateD_(j,k). On the other hand, when the condition D is not satisfied (No;in step S400), the processing proceeds to a step S500.

The step S500 corresponds to the case where the number of simultaneouscalls j exceeds the maximum number of simultaneous calls jmax (refer toformula (2)) by establishing a new call. In this case, the congestioncontrol device 100 executes “call loss processing” for the new call.

Specifically, the congestion control device 100 sets the packet discardrate of the new call to 100%, thereby making the new call substantiallya call loss. Thus, the number of simultaneous calls j is limited to themaximum number of simultaneous calls jmax or less.

3-4. Effects

FIG. 11 is a table showing an example of the relationship between thecall time rank k and the packet discard rate D_(j,k) according to thepresent embodiment. In this example, the line capacity B_(L)=340 kbit/s,the call application band B_(V)=100 kbit/s, the first upper limit valueP_(B)=50%, the second upper limit value P_(C)=25%, and the maximumnumber of simultaneous calls jmax=6 are satisfied. When the number ofsimultaneous calls j is 1 to 3, this corresponds to the case ofcondition A, and no packet is discarded. When the number of simultaneouscalls j is 4, this corresponds to the case of condition B, and the firstpacket discard control is performed. When the number of simultaneouscalls j is 5, this corresponds to the case of condition C, and thesecond packet discard control is performed. When the number ofsimultaneous calls j is 6, this corresponds to the case of condition D,and the third packet discard control is performed.

FIG. 12 shows the relationship between the call time order k and thepacket discard rate D_(j,k) when the number of simultaneous calls j is 5and 6. FIG. 12 also shows the packet discard rate D_(j,k) in the case ofthe comparative example shown in already mentioned FIG. 4 . A state inwhich the number of simultaneous calls j is 5 or 6 (the condition C andthe condition D) is the state in which the packet discard rate D of thefirst call (k=1) in the case of the comparative example has reached thefirst upper limit value P_(B). As shown in FIG. 12 , according to thepresent embodiment, the packet discard rate D_(j,k) of the latest call(k=j) is lower than that in the case of the comparative example. Forexample, when the number of simultaneous calls j is 5, the packetdiscard rate D_(j,k) of the latest call is 0, which is lower than 14% inthe case of the comparative example. When the number of simultaneouscalls j is the maximum number of simultaneous calls jmax (=6), thepacket discard rate D_(j,k) of the latest call is 25% (the second upperlimit value P_(C)), and this is lower that 36.7% in the case of thecomparative example. Thus, the call quality of the latest speech isimproved as compared with the case of the comparative example.Especially, even in a situation where the number of simultaneous calls jbecomes the maximum number of simultaneous calls jmax, the deteriorationin the call quality of the latest call is suppressed.

FIG. 13 is a conceptual diagram showing the relationship between theline bandwidth (B_(L)/B_(V)) and the packet discard rate D_(jmax, jmax)of the latest call in the case of the maximum number of simultaneouscalls jmax. FIG. 13 also shows the case of the comparative example shownin already mentioned FIG. 6 . In the case of the comparative example,there is a situation in which the packet discard rate D_(jmax, jmax) ofthe latest call is considerably close to the first upper limit valueP_(B). On the other hand, according to the present embodiment, thepacket discard rate D_(jmax, jmax) of the latest call is set (limited)to be equal to or less than the second upper limit value P_(C).

Therefore, even in a situation where the number of simultaneous calls jbecomes the maximum number of simultaneous calls jmax, the deteriorationin the call quality of the latest call can be suppressed.

For example, at the time of the disaster, it is imaginable that a largenumber of users will just want to confirm each other's safety. When thecall time is long, there is a high possibility that necessaryinformation has already been transmitted, but when the call time isshort, the possibility is low. According to the present embodiment, thedeterioration of the call quality of the latest call is suppressed sothat important information such as safety confirmation can be conveyedfavorably. After that, as the call carries on and the call qualitylowers, it is expected that the user will end this call. Ending longcalls will free up the line resources and improves the call quality ofother users' calls. Another advantage of the congestion control is thatthe call loss rate will decrease because new calls from users are morelikely to be accepted.

4. Configuration Example of Congestion Control Device

FIG. 14 is a block diagram showing a configuration example of thecongestion control device 100 according to the present embodiment. Thecongestion control device 100 includes a reception interface 110, atransmission interface 120, and an information processing device 130.The reception interface 110 receives packets from outside. Thetransmission interface 120 transmits packets to outside.

The information processing device 130 performs various informationprocessing. For example, the information processing device 130 includesa processor 131 and a storage device 132. The processor 131 performsvarious information processing. For example, the processor 131 includesa CPU (Central Processing Unit). The storage device 132 stores variouskinds of information necessary for processing by the processor 131. Asthe storage device 132, a volatile memory, a non-volatile memory, an HDD(Hard Disk Drive), an SSD (Solid State Drive), and the like areexemplified.

The congestion control program PROG is a computer program executed by acomputer. The processor 131 implements the functions of the informationprocessing device 130 by executing the congestion control program PROG.The congestion control program PROG is stored in the storage device 132.The congestion control program PROG may be recorded in acomputer-readable recording medium. The congestion control program PROGmay be provided via a network.

The information processing device 130 may be implemented using hardwaresuch as an ASIC (Application Specific Integrated Circuit), PLD(Programmable Logic Device), FPGA (Field Programmable Gate Array), andso on.

FIG. 15 is a block diagram showing a functional configuration example ofthe congestion control device 100-1 in the base station 10 side. Thecongestion control device 100-1 includes a reception interface 110-A, atransmission interface 120-A, a reception interface 110-B, and atransmission interface 120-B. The reception interface 110-A receivespackets from the ground network 2. The transmission interface 120-Atransmits packets to the inter-station line 3 or communication network4. The reception interface 110-B receives packets from an inter-stationline 3 or communication network 4. The transmission interface 120-Btransmits packets to the ground network 2.

The congestion control device 100-1 further includes a signal analysisunit 150, a call management unit 160, and a packet transmission controlunit 170. These of the signal analysis unit 150, the call managementunit 160, and the packet transmission control unit 170 are implementedby the information processing device 130.

The signal analysis unit 150 receives a reception packet from thereception interface 110-A. The signal analysis unit 150 analyzes thereception packet and acquires information on the reception packet.Specifically, the signal analysis unit 150 acquires a transmissionsource address, a transmission source port number, a destinationaddress, and a destination port number of the reception packet. Thesignal analysis unit 150 judges whether the reception packet is for acall start, a call end, or others. The signal analysis unit 150 informsthe call management unit 160 of analysis results information indicatingthe transmission source address, the transmission source port number,the destination address, the destination port number, and theclassification (the call start, the call end, others).

The call management unit 160 manages each of the calls handled by thecongestion control device 100. Each call is defined by a combination ofthe source address, the source port number, the destination address, andthe destination port number. The call management unit 160 receives theanalysis results information from the signal analysis unit 150, andgenerates and updates the call management table 200 based on theanalysis results information.

FIG. 16 is a conceptual diagram showing an example of the callmanagement table 200. The call management table 200 has entries forrespective call. Each entry includes a call ID, the source address, thesource port number, the destination address, the destination portnumber, and a call start time.

When the classification of the reception packet is “the start call”, thecall management unit 160 creates an entry for a new call. Thecombination of the source address, the source port number, thedestination address, and the destination port number for the new call isobtained from the analysis results information. The call management unit160 assigns the call ID to the new call session. Further, the callmanagement unit 160 sets the current time to the call start time of thenew call.

When the classification of the reception packet is “the call end”, thecall management unit 160 deletes the entry for this call.

When receiving the reception packet, the signal analysis unit 150inquires the number of simultaneous calls j and the call time order k ofeach call of the call management unit 160. The call management unit 160refers to the call management table 200 and acquires the number ofsimultaneous calls j and the call time order k. At this time, the calltime can be calculated from the current time and the call start time. Asthe call time becomes longer, the call time order k becomes higher. Thecall management unit 160 notifies the signal analysis unit 150 of thenumber of simultaneous calls j and the call time order k of each call.

A packet discard rate determination unit 155 of the signal analysis unit150 determines the packet discard rate D_(j,k) of each call on the basisof the number of simultaneous calls j and the call time order k of eachcall. Then, the signal analysis unit 150 notifies the packettransmission control unit 170 of the packet discard rates D_(j,k) ofeach call.

In the case of executing the call loss processing, the packet discardrate determination unit 155 sets the packet discard rate of the new callto 100%. The signal analysis unit 150 then notifies the call managementunit 160 of the call loss processing execution to the new call. The callmanagement unit 160 deletes the entries for the new call from the callmanagement table 200.

The packet transmission control unit 170 receives the reception packetsfrom the reception interface 110-A. The packet transmission control unit170 discards packets as required in accordance with the discard rateD_(j,k) notified from the signal analysis unit 150. The packettransmission control unit 170 then transmits the packets that were notdiscarded via the transmission interface 120-A.

FIG. 17 is a block diagram showing a functional configuration example ofthe congestion control device 100-2 in the terminal station 20. Thecongestion control device 100-2 has the same configuration as that ofthe congestion control device 100-1 shown in FIG. 15 . However, thedifference is that the reception interface 110-A receives packets fromthe terminal station network 5 while the transmission interface 120-Btransmits packets to the terminal station network 5. The functions ofthe signal analysis unit 150, the call management unit 160, and thepacket transmission control unit 170 are similar to those of thecongestion control device 100-1 shown in FIG. 15 .

REFERENCE SIGNS LIST

-   -   1 IP telephone system    -   2 Ground network    -   3 Inter-station line    -   4 Communication network    -   5 Terminal station network    -   10 Base station    -   20 Terminal station    -   100 Congestion control device    -   110 Reception interface    -   120 Transmission interface    -   130 Information processing device    -   131 Processor    -   132 Storage device    -   150 Signal analysis unit    -   155 Packet discard rate determination unit    -   160 Call management unit    -   170 Packet transmission control unit    -   200 Call management table    -   PROG Congestion control program

1. A congestion control method in an Internet Protocol (IP) telephonesystem, comprising: acquiring a number of simultaneous calls in a firstline shared by a plurality of IP telephones; acquiring a call time ordercorresponding to a length of a call time for each call; and controllinga packet discard rate of each call based on the number of simultaneouscalls and the call time order, wherein controlling the packet discardrate includes: setting the packet discard rate of each call to be equalto or less than a predetermined first upper limit value, setting thepacket discard rate (i) higher for longer call times and (ii) lower forshorter call times, and setting the packet discard rate of a latest callhaving the shortest call time is set to be equal to or less than apredetermined second upper limit value lower than the predeterminedfirst upper limit value.
 2. The congestion control method according toclaim 1, wherein: in a comparison method, the packet discard rate ofeach call is set to be equal to or less than the predetermined firstupper limit value, the packet discard rate is set higher for longer calltimes, the packet discard rate is set lower for shorter call times,further the packet discard rate is set so that the packet discard ratelinearly changes with respect to the call time order, a first call has alongest call time, a first state is a state in which the packet discardrate of the first call in the case of the comparison method reaches thepredetermined first upper limit value, and in the first state, thepacket discard rate of the latest call is set to be lower than that ofthe comparison method.
 3. The congestion control method according toclaim 2, wherein, in the first state, a function of the packet discardrate with respect to the call time order is convex upward.
 4. Thecongestion control method according to claim 2, wherein controlling thepacket discard rate includes, in the first state, based on the packetdiscard rate of the latest call by the comparison method being greaterthan 0 and equal to or less than the predetermined second upper limitvalue, setting the packet discard rate of the latest call to
 0. 5. Thecongestion control method according to claim 2, wherein controlling thepacket discard rate includes, in the first state, based on the packetdiscard rate of the latest call by the comparison method exceeding thepredetermined second upper limit value, setting the packet discard rateof the latest call to the predetermined second upper limit value.
 6. Thecongestion control method according to claim 1, further comprising:based on establishment of a new call causing the number of simultaneouscalls to exceed the maximum number of simultaneous calls, setting thepacket discard rate to 100%.
 7. A non-transitory computer recordingmedium storing a congestion control program, wherein execution of thecongestion control program causes one or more computers to performoperations comprising: acquiring a number of simultaneous calls in afirst line shared by a plurality of Internet Protocol (IP) telephones;acquiring a call time order corresponding to a length of call time foreach call; and controlling a packet discard rate of each call based onthe number of simultaneous calls and the call time order, whereincontrolling the packet discard rate includes: setting the packet discardrate of each call to be equal to or less than a redetermined first upperlimit value, setting the packet discard rate (i) higher for longer calltimes and (ii) lower for shorter call times, and setting the packetdiscard rate of a latest call having the shortest call time to be equalto or less than a predetermined second upper limit value lower than thepredetermined first upper limit value.
 8. A congestion control device inan Internet Protocol (IP) telephone system, comprising: an informationprocessing device, implemented using one or more computing devices,configured to perform operations comprising: acquiring a number ofsimultaneous calls in a first line shared by a plurality of IPtelephones, acquiring a call time order corresponding to a length ofcall time for each call, and controlling a packet discard rate of eachcall based on the number of simultaneous calls and the call time order,wherein the information processing device is configured to: set thepacket discard rate of each call to be equal to or less than apredetermined first upper limit value, set the packet discard rate (i)higher for longer call times and (ii) lower for shorter call times, andset the packet discard rate of a latest call having the shortest calltime is set to be equal to or less than a predetermined second upperlimit value lower than the predetermined first upper limit value.